This invention relates to a paper feed control system in a printer, such as line printer. More specifically, it relates to a paper feed control system in which the feeding operation of a printing paper is controlled by a format tape.
In the printer system, it is known in the art to control the feeding operation of the printing paper by the format tape. One of such examples is disclosed in the U.S. Pat. No. 3,042,178. The typical format tape has twelve channels along the direction of its advance and a plurality of rows perpendicular to the channels. A perforation is punched in the intersection of a preselected row and channel of the format tape, which defines a printing form in the printing paper. The format tape is moved by a motor, such as servo motor, until the perforation is sensed at the senser, and the printing paper is advanced an amount equal to the movement of the format tape. In this case, it is necessary that the perforation should be sensed in synchronism with a line pulse generated every one line advancement of the printing paper. In the type having an encoder directly secured to a paper feeding shaft, it is the general practice to adjust the position of the senser so that the line pulse obtained from the encoder is generated in an approximate midpoint of the perforation.
However, there is an inconvenience in the printer system employing a pulse motor. In such a printer system, the line pulse is not generated from the encoder but generated when a predetermined number of driving pulses applied to the pulse motor is counted. It is now assumed that a four-phase pulse motor is employed, where adjacent two phases are excited and the I-II phases are excited when the power supply is switched on. When one driving pulse is applied to the motor after the power supply is switched on, the II-III phases are excited. In this manner, with one driving pulse the adjacent two phases are excited in turn. The line pulse is assumed to be generated when eight driving pulses are counted. Then, as can be appreciated from FIG. 6, the excitation for the I-II phases will take place twice during one line advancement of the printing paper. Therefore, depending on which I-II phases are excited at the time when the power supply is switched on, the generation of the line pulse may be displaced an amount corresponding to a half line of the printing paper. As a result, the line pulse may be generated in the position between the adjacent lines to be printed, whereby the line pulse is not generated in synchronism with the perforation in the format tape.
Shown in FIG. 3 is a timing chart explaining the paper feeding operation according to the pulse motor. Driving pulses for switching the excited phases of the pulse motor are generated when a feed signal for feeding the printing paper is in "1" state and the pulse motor is driven in response to the driving pulses. When the eighth driving pulse is generated, one line pulse is generated. The thus generated line pulse causes to stop the feeding of the printing paper provided that the perforation signal is in "1" state. That is, when the perforation signal is in "1" state and immediately after the line pulse is generated, the feed signal is put in "0" state, whereby the pulse motor is stopped after the rotation responsive to the eighth driving pulse.